In many cases of severe disease or injury of the bones of the thigh or leg in the region of the knee joint one mode of treatment is to remove the knee joint and part of the adjacent shaft of either the femur or tibia or both and implant a prosthesis. The loss of many of the ligaments and tendons that impart stability to the anatomical knee joint means that the prosthesis must be designed to restrict motions that are normally restricted by those tissues. Various designs of constrained knee joint prostheses have been proposed, some examples being described and shown in the following U.S. Pat. Nos. 3,696,446; 3,765,033; 3,824,630; 3,837,009; and 4,112,522.
It is well-known (see, for example, U.S. Pat. No. 3,837,009) that a simple hinge is a poor choice for a constrained knee joint prosthesis, inasmuch as the anatomical knee joint provides not only for antero-posterior flexure between the femur and tibia but for axial rotation and latero-medial flexure (lateral angulation). It is also recognized that wear of articulating surfaces that are subject to relative movement and large load transfers is minimized by avoiding metal-to-metal contact and making one of the surfaces of plastic. This concept has not ordinarily been extended to control surfaces where loads are minimal and sliding contact sporadic.
Bone and joint replacements for severely diseased or injured thighs or legs where the femoral or tibial shafts are involved, a common case being bone cancer, often call for custom-made prostheses. The costs of designing and fabricating a custom prosthesis are considerable. Moreover, some conditions of the thigh or leg that govern the particular design re not always fully known in advance of surgery, so it is possible that the costly custom prosthesis on hand at surgery may not be optimally suited for the patient.